A growing number of (commercial) communication systems, such as those providing audio programming, including but not limited to music, educational, sports, etc., program material, are being implemented as satellite link-based, store and forward digital audio broadcast systems. In this type of system, the general architecture of which is diagrammatically illustrated in FIG. 1, real-time digital audio program material is broadcast from a network headend facility 10 over a satellite communication link 20 to a number of geographically dispersed users (such as affiliate radio stations) 30. As it is being received, this headend-sourced program audio material is immediately rebroadcast to an associated local station audience, as through conventional radio broadcast transmission equipment, and the like.
Concurrent with the real-time satellite transmission of the to-be-rebroadcast program material, additionally unique information (e.g. local commercials, specific station identifiers, delayed programming, etc.) may be downloaded from the headend station to its affiliate radio station receivers and stored in a local digital storage device (e.g. hard disk drive, solid state flash memory, and the like) for later use by the affiliate station. In addition, from time-to-time, the headend may forward (or the operator of the local station may generate) commands, that are used to trigger the performance of one or more functions, such as but not limited to, recording the real-time broadcast digital audio stream, operating audio mixers, managing the digital storage media, initiating relay switch closures, playing back previously stored material, forwarding stored files to the local network, etc. When stored material is to be played back, it may be inserted or interleaved with or overlaid on the real-time programming or forwarded to an external device as the radio station.
For this purpose, the network headend facility 10 typically comprises a digital audio encoder 11, which is operative to encode or convert real-time audio content into a prescribed digitally encoded format (such as motion picture expert group (MPEG) format) for transmission over the satellite link. The encoded real-time digital audio stream produced by encoder 11 is coupled as one input to a multiplexer 12, the aggregate digital output of which is applied to a modulator 13 for application to a transmitter 14 and transmission thereby over the satellite link 20 to various store and forward receiver stations 30. Additional inputs to the multiplexer 12 may include a real-time control channel from a network automation system (which will from time-to-time issue commands to affiliate stations to perform various actions), a user data channel, audio files supplied from an audio file server 14, as well as digital information supplied from one or more other sources (not shown).
The equipment employed at a respective affiliate radio station 30 is comprised principally of a receiving satellite antenna subsystem 31, the output of which is coupled to a store and forward receiver 32. In its most basic application, the receiver may output received audio programming directly to an attendant rebroadcasting unit 33, such as one containing conventional radio broadcast transmission equipment, and the like, for real-time rebroadcast of the audio programming, as it is received from the headend to an associated local station audience. In addition, the receiver may be connected to an automation system, which may accept signaling inputs from or provide signal outputs to the receiver. Also, the receiver may be connected to a local area network (LAN) for transferring audio files to various users served by the station.
For the most part, the intended operation of the satellite link-based store and forward system of the type shown in FIG. 1 has the receiver sites 30 controlled by the automation network headend facility 10. A typical operation to be performed by a receiver is to implement a station break, which customarily requires the execution of a prescribed sequence of events. As a non-limiting example, to implement a sixty second station break having two commercial messages or ‘spots’ and a station identification (ID) message, the following actions may be performed:
Momentarily close a relay to signal the beginning of the station break;
Maintain another relay closed during the break;
Transition the input to an audio mixer from the real-time feed from the headend to the output of a decoder through which previously recorded or stored (station break) material is played back;
Maintain the audio mixer's settings for the decoder feed for a prescribed time interval;
Play back a locally unique file (e.g., a ten second recorded file) containing the specific local station ID;
Play back a commercial spot (e.g. a thirty second recorded file);
Play back a ‘liner’ for the network (e.g. a twenty second recorded file); and
Transition the input to an audio mixer from the output of a decoder back to the real-time feed from the headend.
Now although the each of the eight actions listed above for a typical sixty second station break is a relatively simple function, it is imperative that they be executed with a very high degree of timing accuracy, in order to ensure that they be perceived to the listener as occurring instantaneously (without delay). If not, for example if there were a two second delay between successive file playbacks, the effect would be very noticeable to the listening audience and be perceived as a non-professional sound to the station's programming. Furthermore, the insertion of locally unique material must be seamless such that the local station appears to be locally produced with live sounding local “on air” personalities.
Associated with this delay problem in an individual receiver is the probability that different receivers in the network will be simultaneously performing different functions (e.g. playing different files). Yet, all receivers must be able to perform their operations with perceptually no delay, irrespective of the number of different actions being performed. Namely, all actions must be performed with minimal delay or timing uncertainty.
In addition to the likelihood that different receivers will be simultaneously performing different functions, there is also the requirement that different receivers perform different actions, so as to allow affiliate stations to insert files whose content is appropriate to their locality, time zone, audience, etc. This enables a network affiliate station to target commercials and other content to that station's listening audience at the appropriate time, but still rebroadcast the network programming. In order to accomplish this, the system must implement some form of group addressing for download content as well as for commands. Examples of groups include time zones, states, FM stations vs. AM stations, rural areas vs. suburbs, etc. Receivers must also be capable of belonging to multiple groups.
In the course of satisfying the criticality of the timing of such command-response actions being performed by the receiver (which take place only occasionally), it is undesirable to employ more than a relatively small amount of the available bandwidth to command these operations, in order to avoid an unacceptably high system overhead cost. Moreover, as pointed out above, in some instances, it may be desired that the local affiliate station, rather than the headend, generate the commands for receiver operation. As a non-limiting example, the playback of a local weather report from a predetermined audio output port of the receiver may be triggered by the station operator activation of a push-button switch. Another example would be for the affiliate station to record a live newscast sourced from the headend for later broadcast.